Phenol-formaldehyde (PF) resins, as well as PF resins extended with urea (PFU resins), have been the mainstays of porous fiberglass material technology over the past several years. Such resins are inexpensive and provide the cured fiberglass insulation product with excellent physical properties.
One common type of porous fiberglass material is fiberglass insulation. Generally, fiberglass insulation is shipped in a compressed form to facilitate transportation and reduce costs. When the compressed bundles of fiberglass are used at a job site, it is important that the compressed fiberglass product recover a substantially amount of it pre-compressed thickness. If not, the product will suffer a decrease is its thermal insulation and sound attenuation properties. Fiberglass insulation made with PF and PFU resins is able to recover most of its pre-compressed thickness, thus contributing to the wide acceptance of these resins in this application.
Fiberglass insulation is typically made by spraying a dilute aqueous solution of the PF or PFU resin adhesive binder onto glass fibers, which are generally hot from being recently formed. A mat or blanket of the resin-treated fibers is formed from the hot fibers and the mat or blanket is heated to an elevated temperature in an oven to complete the cure of the adhesive resin binder.
Manufacturing facilities using PF and PFU resins as the main adhesive binder component for porous fiberglass material recently have invested in pollution abatement equipment to minimize the possible exposure of workers to formaldehyde emissions and to meet Maximum Achievable Control Technology (MACT) requirement Standards during the manufacturing of the fiberglass insulation. This technology has successfully reduced exposure to formaldehyde during the manufacturing process.
Reducing formaldehyde emissions in the manufacturing environment, however, does not necessarily reduce formaldehyde emissions from the resulting insulation product. Producing a product having a reduced tendency to emit formaldehyde remains a goal of manufacturers producing products bonded with formaldehyde-containing resins. The fiberglass insulation industry is very concerned with formaldehyde emissions from their finished product due to end user customer concerns about indoor air quality. Fiberglass producers that have continued to use phenol-formaldehyde resins have been moving to obtain certification by a third-party organization called “Green Guard” which tests the emissions of products, which is possible to obtain when the product emits less than 50 ppb formaldehyde. However, the “gold standard” for certification is that the amount of emissions from the product is “below quantifiable limits.” In short, it has been an unrealized goal to date to obtain below quantifiable limits of formaldehyde in a porous fiberglass material.
Attempts have been made to scavenge formaldehyde emissions in a building environment, where the formaldehyde emissions emanated from a product having a formaldehyde-emitting binder thereon. As one example, U.S. Pat. No. 4,409,375, the disclosure of which is incorporated herein in its entirety by this reference for the discussion of the aldehyde scavenging aspect therein, discloses the use of an aqueous bisulfite solution to reduce the presence formaldehyde emissions. In the '375 patent, six pans (totaling 2 gallons of a 1% aqueous bisulfite solution were placed in a room. After 4 days, the amount of formaldehyde emissions in the room decreased to a minimum amount. The method disclosed in the '375 patent only dealt with emissions that were released into the room; the substrate remained a formaldehyde emitter even with the bisulfite in the room. The formaldehyde-emitting material in the '375 patent could not have absorbed the bisulfite due to the high density thereof. Thus, the method of the '375 patent would not be effective in stopping formaldehyde emissions.
Another option of reducing formaldehyde emissions in the field of fiberglass insulation has been described in U.S. Pat. No. 5,578,371, the disclosure of which is incorporated herein in its entirety by this reference for the discussion of the formaldehyde reduction therein. However, the emissions reduction taught is directed towards reducing formaldehyde emissions in the manufacturing process, not in the finished product. In the '371 patent, a scavenger, which is a bisulfite material, is mixed with the uncured binder before being sprayed onto the fiberglass, during the manufacture of the fiberglass insulation. In evaluating the method of the '371 patent, the inventors herein have determined that the bisulfite becomes incorporated into the binder during cure, thus reducing the amount of binder available to form cross-links, especially at higher levels of scavenger (e.g., greater than 5% by weight of binder solids). Further, the inventors herein have determined that the method of the '371 patent has minimal, if any, affect on the amount of formaldehyde emitted from the cured binder.
As an alternative to PF and PFU resins, certain formaldehyde free formulations have been developed for use as an adhesive binder for making fiberglass insulation products. Such technology potentially holds the promise of lowered formaldehyde emission from the ultimate product. Unfortunately, however, implementation of the commercial technology that is currently available is considerably more expensive, in terms of both raw material cost and equipment upgrades, relative to the PF and PFU resins that have been the mainstay of the fiberglass insulation industry.
There thus remains an unmet need to have a way to reduce emissions from a formaldehyde-emitting binder that has been cured.